Pyrolysis-based fuel processing method and apparatus

ABSTRACT

The method for generating a hydrogen-rich stream from hydrocarbon fuels, ultimately to produce hydrogen gas, involves the following two steps performed in a cyclic fashion: (1) pyrolysis of the hydrocarbon fuel to obtain a carbon-rich fraction and a hydrogen-rich fraction; and (2) oxidation of the carbon-rich fraction, or a portion of it, for heat generation. The method involves the following optional steps: (3) steam gasification of part of the carbon-rich fraction to produce additional amounts of hydrogen and carbon monoxide; (4) water-gas shift reaction to convert carbon monoxide to carbon dioxide with the simultaneous formation of additional amounts of hydrogen; and (5) steam reforming of light hydrocarbons that may be produced in step (1) to produce more hydrogen and carbon monoxide.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/216,888, filed Jul. 7, 2000, in the names of theinventors designated herein and bearing the same title.

STATEMENT REGARDING GOVERNMENT INTEREST

[0002] The United States Government has rights in this invention underNational Science Foundation grant No. DMI-9632781.

BACKGROUND OF THE INVENTION

[0003] Fuel cells which are currently of commercial interest operate onstreams of pure or nearly pure hydrogen, which is not readily availablein most vehicles. Neither is a source of pure hydrogen convenient orsafe to carry on board commercial trucks, buses or other vehicles.However, liquid hydrocarbons, such as diesel fuels, are easily availableand their handling, storage and distribution are well developed.Consequently, the large-scale use of fuel cells is expected to requireconversion of liquid fuels into a stream of pure hydrogen orhydrogen/CO₂ mixtures, with only trace amounts of CO or sulfurimpurities. This conversion will require a multi-step process to becarried out on board vehicles.

[0004] Dramatic progress has been observed in fuel-cell technologies inrecent years. A prototype fuel cell-powered bus has been built byBallard Power Systems for Vancouver's BC Transit. In this bus,compressed hydrogen is used to fuel the cells, which has raised concernsabout passengers' safety. In a different venture, Argonne NationalLaboratory has built three prototype buses running on fuel cells. Thesevehicles operate with the diesel engine replaced by an electric engine,a phosphoric-acid fuel cell, and an on-board reformer. The role of thereformer is to convert liquid methanol into hydrogen in situ, and thusto avoid the necessity of carrying pressurized hydrogen. It isinteresting to note that Argonne's fuel cell and the reformer are notmuch larger than the diesel engine they replaced. The fact that methanolis not currently a widely used fuel poses obvious limitations. There arealso concerns related to long-term viability as well as corrosivenessand toxicity of methanol.

[0005] The development of an on-board system capable of convertinghydrocarbon fuels, such as gasoline, diesel, JP-5, natural gas, etc.,into a stream of hydrogen-rich gas would make it possible to powervehicles using standard fuels in combination with fuel cells. This wouldgreatly accelerate the introduction of fuel-cell technologies into masstransit and help reduce air pollution in urban centers (particulates,NO_(x), CO, and unburned hydrocarbons). The advantage of on-board fuelprocessing is clear: the utilization of conventional fuels at improvedefficiency, lower pollution levels, and zero noise.

[0006] Partial Oxidation

[0007] One current approach to the conversion of standard liquid fuelsinto hydrogen is partial oxidation (POX) of the liquids to produce soot,carbon oxides and hydrogen. The reaction is normally carried out withouta catalyst in the temperature range 1100-1500° C. This technology issimilar to the process used in the manufacture of carbon black (Austin,G. T., Shreve's Chemical Process Industries, Fifth edition, McGraw-Hill,New York, 1984). A number of projects are currently under way in whichfuel processors based on partial oxidation are being developed(Preprints of the Annual Automotive Technology Development Contractors'Coordination Meeting, PNGV Workshop on Fuel Processing for ProtonExchange Membrane (PEM) Fuel Cells, Dearborn, Mich., Oct. 23-27, 1995,Office of Transportation Technologies, U.S. Department of Energy,Washington, D.C., 1995; Preprints of the Annual Automotive TechnologyDevelopment Contractors' Coordination Meeting, vol. 1, Dearborn, Mich.,Oct. 23-27, 1995; “Recent Advances in Fuel Cells,” M. A. Wójtowicz,Symposium Organizer, in ACS Div. of Fuel Chemistry Prepr. 44 (4), pp.972-997, 1999; “Hydrogen Production, Storage, and Utilization,” C. E.Gregoire-Padro and F. S. Lau, Symposium Organizers, in ACS Div. of FuelChemistry Prepr. 44 (4), pp. 841-971, 1999). The advantages of partialoxidation include simplicity, exothermicity of the process, sulfurtolerance, rapid start-up, rapid response to load changes, andcompactness. However, partial oxidation produces relatively smallamounts of gaseous hydrogen, which is diluted with nitrogen, largeamounts of carbon oxides and soot, and the efficiency of fuelutilization is relatively low.

[0008] Steam Reforning

[0009] A second approach is based on steam reforming of hydrocarbonfuels according to the following reaction:

C_(n)H_(m) +nH₂O→nCO+(n+m/2) H₂  (A)

[0010] wherein n and m are typically in the range 1-20 and 4-42,respectively.

[0011] Since the above reaction is endothermic, the unreacted hydrogenfrom the fuel cell is usually burned to provide process heat. Thereaction occurs over a catalyst in the temperature range 700-1000° C.

[0012] Since proton-exchange membrane (PEM) fuel cells, which aretypically used in transportation applications, are intolerant to carbonmonoxide, the latter species present in the product gas is often shiftedto carbon dioxide according to the following reaction:

CO+H₂O

>CO₂+H₂  (B)

[0013] Shift conversion is usually carried outin two stages: ahigh-temperature stage followed by a low-temperature stage. The formerstage promotes high reaction rates, whereas the low-temperature stageincreases the yield. Since the water-gas shift reaction is exothermic,inter-stage cooling is often implemented. In high-temperature fuelcells, CO can be oxidized to CO₂ directly, and no shift reaction isnecessary.

[0014] Steam reforming is a well-established large scale technology, butdesign, construction, and operation of compact reformers is quite achallenge. Common feedstocks for steam reforming are natural gas,propane and butane. The use of heavier feedstocks, such as naphtha, isdifficult, and this problem can be only partly alleviated by the use ofspecially prepared catalysts (Austin, G. T., Shreve's Chemical ProcessIndustries, Fifth edition, McGraw-Hill, New York, 1984). In most cases,a desulfurization step is required upstream of the reformer to protectcatalyst beds from deactivation.

[0015] Autothermal Reforming

[0016] Autothermal reforming (ATR) is a hybrid approach involvingendothermic steam reforming combined with partial oxidation for heatgeneration. The fuel is mixed with a mixture of steam and air,preheated, and fed into a catalytic reactor. Proper control of thesteam-to-fuel ration is required to avoid coke formation, and thereaction usually occurs at 650-700° C. The effluent is typically sent toa shift reactor prior to entering the fuel cell. The advantages of ATRinclude compactness, and nitrogen dilution is the main disadvantage. Theefficiency of ATR is lower than that of steam reforming but higher thanPOX.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a diagram providing an overview of a reaction schemeembodying the present invention.

[0018]FIG. 2 is a flow diagram of a system embodying the invention,comprising a diesel processor, a fuel cell, and auxiliary components(steam reformer, shift reactor, sulfur and CO removal units, etc.).

SUMMARY OF THE INVENTION

[0019] It is a broad object of the present invention to provide a novelmethod for producing a stream of hydrogen-rich gas, and thereby forproducing hydrogen gas, from a hydrocarbonaceous material.

[0020] It is also an object of the invention to provide a power systemwherein hydrogen gas for use in a fuel cell is produced from ahydrocarbonaceous material, and wherein the system may be self-containedand implemented in a transport vehicle.

[0021] It has now been found that certain of the foregoing and relatedobjects of the invention attained by the provision of a method forproducing hydrogen gas from a hydrocarbonaceous material, using reactionapparatus that includes means for absorbing and releasing thermal energyand having a heat-transfer surface. The method comprises the followingsteps, carried out cyclically:

[0022] (a) bringing a quantity of a hydrocarbonaceous material intocontact with the surface of the means for absorbing and releasingthermal energy, heated to a temperature T_(max), to effect pyrolysisthereof and thereby to produce quantities of solid carbon-rich residueand hydrogen gas;

[0023] (b) effecting combustion of at least a first portion of thequantity of the carbon-rich residue produced in the pyrolysis step; and

[0024] (c) utilizing at least a portion of the thermal energy producedin the combustion step to heat the means for absorbing and releasingthermal energy to T_(max), for effecting the pyrolysis step in the nextsucceeding cycle of the method.

[0025] The method will preferably include the additional step of (d)effecting steam gasification of a second portion of the solidcarbon-rich residue produced in the pyrolysis step and deposited on theheat transfer surface. In accordance therewith, steam may be introducedinto the reaction apparatus subsequent to the pyrolysis step, forreaction with the second portion of the carbon-rich residue to effectthe steam gasification step, with the sensible heat of the means forabsorbing and releasing thermal energy supplying the heat necessary; theportion of thermal energy produced in the combustion step and used forheating the means for absorbing and releasing thermal energy would, insuch instances, be sufficient to supply the energy necessary for boththe pyrolysis step and also the steam gasification step.

[0026] In most embodiments of the method a quantity of carbon monoxideis produced, directly or indirectly, from the hydrocarbonaceousmaterial, and the method desirably includes the additional step of (e)effecting a water-gas shift reaction, utilizing at least a portion ofthe quantity of carbon monoxide produced, so as to produce carbondioxide and an additional quantity of hydrogen gas. The method may alsoinclude the additional step of (f) effecting steam reforming of gaseoushydrocarbons produced in the pyrolysis step, preferably using thermalenergy produced in the combustion step. The means for absorbing andreleasing thermal energy may comprise a bed of a catalyst that iseffective for promoting pyrolysis of the hydrocarbonaceous material.

[0027] Other objects of the invention are attained by the provision of apower system comprising a fuel cell, which utilizes hydrogen for powergeneration, and reaction apparatus for producing hydrogen gas,operatively connected for delivering hydrogen gas produced thereby tothe fuel cell. The reaction apparatus employed will include: means forabsorbing and releasing thermal energy and having a heat transfersurface; means for introducing a hydrocarbonaceous material into theapparatus and for depositing the material upon the heat transfer surfacethereof, for effecting pyrolysis of the material; and means forintroducing an oxygen-containing gas into the apparatus for effectingcombustion of carbon produced by pyrolysis of the depositedhydrocarbonaceous material, and for thereby delivering thermal energy tothe means for absorbing and releasing thermal energy.

[0028] In preferred embodiments the system will be self-contained, andwill additionally include means for storing a supply ofhydrocarbonaceous material, operatively connected to the means forintroducing. Such a system may be part of a transportation vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The fuel-conversion process is divided into several phases thatpreferably take place in the same reactor. The reactor mass, includingpacking (which will preferably comprise a catalyst bed), is used as aheat-transfer medium in such a way that the heat required by endothermicreactions is provided from preceding exothermic cycles. Thus, thereactor mass, which may comprise the reactor walls, catalyst bed,refractory liners, any suitable packing that increases the thermalcapacity of the system, etc., constitutes the means for absorption andrelease of heat. The operation of the fuel processor is described insteps a-d below. FIG. 1 provides an overview of reaction pathways.

[0030] At a cold start (not included in FIG. 1), the fuel is burned withair within the reactor volume until the maximum temperature of thereactor mass T_(max.) is reached. The exhaust gases from this cycle arediscarded. As an alternative, a rapid start-up could be achieved by theinitial heating of the reactor with a hydrogen flame. The hydrogenneeded for start-up would be stored in a small hydrogen reservoir.

fuel+O₂→CO₂ and H₂O (heat generation for cold start-up)  (1)

or

H₂O½O₂→H₂O (heat generation for cold start-up)  (2)

[0031]  It should be noted that any other suitable way of warming up thereactor can be used, which will be apparent to those skilled in the art.

[0032] a) In the next step, the air supply is cut off and the fuel isthermally or catalytically cracked (pyrolyzed) on hot reactor surfacesto produce carbon and hydrogen as the main products. Some quantities oflight hydrocarbons (mostly methane) and a heavy-hydrocarbon deposit arealso formed. An optimal product distribution would be carbon andhydrogen, with only small amounts of light and heavy hydrocarbons. Ifthe amount of light hydrocarbons produced is small, the product gasescould be utilized by the fuel cell directly. Otherwise, a reforming stepmay be desirable to convert light hydrocarbons to hydrogen.

fuel→H₂+C+C⁻⁴+heavy HC's (fuel pyrolysis)  (3)

C⁻⁴+H₂O→H₂+CO (reforming)  (4)

[0033]  where C⁻⁴ denotes light hydrocarbons with four or fewer carbonatoms, and HC's stands for hydrocarbons.

[0034]  In step (b), temperature drops from T_(max) to T₁.

[0035] b) The next step involves endothermic steam gasification of thecarbon-rich deposit to produce CO and H₂. The heat for this reaction isprovided by the hot reactor core, or the catalyst bed, the temperatureof which drops from T₁ to T_(min).

C+heavy HC's+H₂O→H₂+CO (steam gasification)  (5)

[0036]  Before entering the fuel cell, the gaseous effluent may betreated with steam in a shift reactor to produce carbon dioxide and morehydrogen:

CO+H₂O→CO₂+H₂ (water-gas shift)  (6)

[0037] In principle, the water-gas-shift reaction may occur inherentlyduring the gasification step if excess amounts of steam are present inthe system. Through proper design, the water-gas-shift reaction may beintegrated with the gasification step and take place within the samereactor. The water-gas shift reaction is mildly exothermic.

[0038] c) In the last cycle, the reactor core temperature is raised backto T_(max.) by burning the remaining carbon in air or oxygen.

C+heavy HC's+O₂→CO₂+CO (combustion)  (7)

[0039] The exhaust gases of this cycle may be discarded, or the CO maybe shifted to CO₂ and additional hydrogen via reaction 6.

[0040] Stages (b), (c), and (d) will be referred to as pyrolysis (orfuel cracking), gasification, and oxidation (or carbon burn-out, orcombustion), respectively.

[0041] It should be appreciated that the above steps may be carried outin a single reactor or in multiple reactors. For example, fuelpyrolysis, steam gasification, and residue combustion may take place inthe same reactor, whereas the water-gas shift reaction is implemented ina separate reactor. In certain embodiments of the invention, however(such as to provide a self-contained installation or transport vehicle),all the above steps will desirably (or necessarily) be integrated withina single reactor system.

[0042] It should also be pointed out that fuel pyrolysis (reaction 3)and the combustion of the carbon-rich residue (reaction 7) are thenecessary steps of the process, whereas the remaining steps are optionalalbeit, to a greater or lesser extent, preferred. In general, theinclusion of the gasification step, steam reforming, and water-gas shiftincreases the efficiency of the fuel processor at the expense ofincreased system complexity. In addition, it should be noted that:

[0043] T_(min) is generally determined by the condition that enoughcarbon-rich deposit must be left so that the temperature can be raisedagain to T_(max) in the carbon burnout step d. Another constraint onT_(min) is of a kinetic nature: if the temperature drops too much, thesteam gasification reaction becomes unacceptably slow, and the reactortemperature has to be raised.

[0044] The above scheme can be implemented with and without catalysts.

[0045] The process can be used for the processing of gaseous, liquid,solid, and mixed hydrocarbon feedstocks.

[0046] The products of the exothermic step (combustion) can becompletely discarded, thereby reducing the load on the water-gas shiftreactor. The secondary processing can be further simplified if thoroughcracking of the fuel to carbon and hydrogen can be effected, with onlynegligible amounts of light hydrocarbon gases produced. In such a case,the steam-reforming step is unnecessary. On the other hand, theutilization of the water-gas shift and C₄ reforming steps leads toimproved system efficiency. High flexibility of the proposed processwill be appreciated.

[0047] The use of multiple cycles involving high temperatures is thoughtto be feasible. It should be noted that the internal-combustion enginedoes involve multiple strokes occurring at high frequencies, highpressures, and at elevated temperatures. It is expected that theengineering of the fuel processor can be readily handled by thoseskilled in the art.

[0048] An example of a reaction scheme embodying the invention is shownin FIG. 1 for the case of diesel processing at about 1100° C. At thistemperature, the main pyrolysis products are found to be hydrogen,carbon residue (mostly carbon), and methane. Simplified reactionstoichiometry is given below.

[0049] Diesel Pyrolysis: $\begin{matrix}{{C_{n}H_{m}}\underset{\Delta}{\rightarrow}{{xH}_{2} + {\frac{m - x}{4}{CH}_{4}} + {\left( {n - \frac{m - x}{4}} \right)C}}} & (8)\end{matrix}$

[0050] Char Gasification: $\begin{matrix}\left. {{{p\left( {n - \frac{m - x}{4}} \right)}C} + {{p\left( {n - \frac{m - x}{4}} \right)}H_{2}O}}\rightarrow{{{p\left( {n - \frac{m - x}{4}} \right)}H_{2}} + {{p\left( {n - \frac{m - x}{4}} \right)}{CO}}} \right. & (9)\end{matrix}$

[0051] Char Combustion: $\begin{matrix}\left. {{{q\left( {1 - p} \right)}\left( {n - \frac{m - x}{4}} \right)C} + {{q\left( {1 - p} \right)}\left( {n - \frac{m - x}{4}} \right)O_{2}}}\rightarrow{{q\left( {1 - p} \right)}\left( {n - \frac{m - x}{4}} \right){CO}_{2}} \right. & \text{(10a)} \\\left. {{\left( {1 - q} \right)\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right)C} + {\frac{1 - q}{2}\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right)O_{2}}}\rightarrow{\left( {1 - q} \right)\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right){CO}} \right. & \text{(10b)}\end{matrix}$

[0052] Water-gas Shift (CO from Char Gasification): $\begin{matrix}\left. {{{{yp}\left( {n - \frac{m - x}{4}} \right)}{CO}} + {{{yp}\left( {n - \frac{m - x}{4}} \right)}H_{2}O}}\rightarrow{{{{yp}\left( {n - \frac{m - x}{4}} \right)}H_{2}} + {{{yp}\left( {n - \frac{m - x}{4}} \right)}{CO}_{2}}} \right. & \text{(11a)} \\\left. {\left( {1 - y} \right){p\left( {n - \frac{m - x}{4}} \right)}{CO}}\rightarrow{\left( {1 - y} \right){p\left( {n - \frac{m - x}{4}} \right)}{CO}} \right. & \text{(11b)}\end{matrix}$

[0053] Methane Reforming: $\begin{matrix}\left. {{r\frac{m - x}{4}{CH}_{4}} + {r\frac{m - x}{4}H_{2}O}}\rightarrow{{3r\frac{m - x}{4}H_{2}} + {r\frac{m - x}{4}{CO}}} \right. & \text{(12a)} \\\left. {\left( {1 - r} \right){CH}_{4}}\rightarrow{\left( {1 - r} \right){CH}_{4}} \right. & \text{(12b)}\end{matrix}$

[0054] Water-gas Shift (CO from Methane Reforming): $\begin{matrix}\left. {{{zr}\frac{m - x}{4}{CO}} + {{zr}\frac{m - x}{4}H_{2}O}}\rightarrow{{{zr}\frac{m - x}{4}H_{2}} + {{zr}\frac{m - x}{4}{CO}_{2}}} \right. & \text{(13a)} \\\left. {\left( {1 - z} \right)r\frac{m - x}{4}{CO}}\rightarrow{\left( {1 - z} \right)r\frac{m - x}{4}{CO}} \right. & \text{(13b)}\end{matrix}$

[0055] Water-gas Shift (CO from Char Combustion): $\begin{matrix}\left. {{{s\left( {1 - q} \right)}\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right){CO}} + {{s\left( {1 - q} \right)}\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right)H_{2}O}}\rightarrow{{{s\left( {1 - q} \right)}\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right)H_{2}} + {{s\left( {1 - q} \right)}\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right){CO}_{2}}} \right. & \text{(14a)} \\\left. {\left( {1 - s} \right)\left( {1 - q} \right)\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right){CO}}\rightarrow{\left( {1 - s} \right)\left( {1 - q} \right)\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right){CO}} \right. & \text{(14b)}\end{matrix}$

[0056] Notation

[0057] p—fraction of char gasified

[0058] (1−p)—fraction of char combusted$\frac{q}{1 - q} - {{{CO}_{2}/{CO}}\quad {ratio}\quad {in}\quad {combustion}\quad {products}}$

[0059] y—fraction of gasification CO shifted

[0060] s—fraction of combustion CO shifted

[0061] r—fraction of CH₄ reformed

[0062] z—fraction of CO from CH₄ reforming shifted

[0063] Overall Reaction Stoichiometry $\begin{matrix}{{{\left. {{{{{{{\left. {{C_{n}H_{m}} + {\left\{ {{\left\lbrack {{p\left( {1 + y} \right)} + {{s\left( {1 - q} \right)}\left( {1 - p} \right)}} \right\rbrack \left( {n - \frac{m - x}{4}} \right)} + {{r\left( {1 + z} \right)}\frac{m - x}{4}}} \right\} H_{2}O} + {\frac{1 + q}{2}\left( {1 - p} \right)\left( {n - \frac{m - x}{4}} \right)O_{2}}}\rightarrow{{\left\{ {\frac{x}{2} + {\left\lbrack {{p\left( {1 + y} \right)} + {{s\left( {1 - q} \right)}\left( {1 - p} \right)}} \right\rbrack \left( {n - \frac{m - x}{4}} \right)} + {{r\left( {3 + z} \right)}\frac{m - x}{4}}} \right\} H_{2}} +} \right.\quad}\quad}{\quad{\left\lbrack {\left( {n - \frac{m - x}{4}} \right)\left\{ {{\left( {1 - p} \right)\left\lbrack {q + {s\left( {1 - q} \right)}} \right\rbrack} +}\quad \right.{yp}} \right\} +}\quad}\left. \quad{{zr}\frac{m - x}{4}} \right\rbrack {CO}_{2}} +}\quad}\left\{ {{\left( {n - \frac{m - x}{4}} \right)\left\lbrack {{p\left( {1 - y} \right)} +}\quad \right.}\left( {1 - q} \right)\left( {1 - p} \right)\left( {1 - s} \right)} \right\rbrack} + {{r\left( {1 - z} \right)}\frac{m - z}{4}}} \right\} {CO}}\quad} + {\left( {1 - r} \right){\quad{\frac{m - x}{4}{CH}_{4}}}}} & (15)\end{matrix}$

[0064] Specific advantages of the system of the invention include:

[0065] The pyrolysis step “splits” the original hydrocarbon feedstock(e.g., diesel fuel) into a carbon-rich fraction (solid and/or heavyliquid) and a hydrogen-rich fraction (gas).

[0066] The separation of these fractions occurs spontaneously.

[0067] The heat-generating step involves combustion of the carbon-richfraction, without the loss of hydrogen. This is in contrast to the POXand ATR reactors where carbon and hydrogen are combustedindiscriminately. This selectivity in the heat generating step leads tosuperior efficiency of the process as compared with POX and ATRreactors.

[0068] The stream of hydrogen-rich gas resulting from the process iseither undiluted or the level of nitrogen dilution is lower than in thecase of POX and ATR.

[0069] The steam-gasification of the carbon residue is an additionalsource of hydrogen originating from water. This source of hydrogen isnot present in POX and ATR processes.

[0070] The water-gas shift reaction also produces additional amounts ofhydrogen from water. This source of hydrogen is present in the POX andATR processes.

[0071] Yet another source of additional hydrogen is the reforming stepin which light hydrocarbons react with steam to produce hydrogen and CO(reaction 4).

[0072] A description of experiments carried out to demonstrate theinvention is given below. Although the invention can be used inconjunction with diverse hydrocarbon fuels, the experiments describedbelow were performed on diesel fuel, which is probably one of the mostchallenging fuels to process.

[0073] Four bench scale, fixed-bed reactors were designed andconstructed, with diameters ranging from 1″ to 1.5″, and with differentdesigns of the fuel-injection assembly. The experimental systemconsisted of a tubular reactor, water and diesel injection section, gasmanifold, and a gas-analysis section. The entire system was computercontrolled, which allowed for automated, unattended operation throughoutmany cycles.

[0074] Each reactor was heated externally using a tube furnace, andfurnace temperature and inlet pressure were recorded on a continuousbasis. A high-pressure, dual-cylinder metering pump (Eldex A-30-S) wasused for fuel delivery, and another metering pump was utilized for waterinjection. Computer controlled valves provided automatic switching fromdiesel to water at the end of the diesel-cracking stage. Both pumps wereequipped with by-pass loops to ensure smooth, trouble-free operation. Asmall stream of nitrogen was used to carry the liquid (diesel or water)aerosol into the reactor, and either air or oxygen was used to bumresidual carbon in the oxidation stage. The flow of gases at the reactorinlet was controlled by means of computer-interfaced solenoid valves.The flow rate of the gas effluent at the reactor outlet was measuredusing a digital volumetric flow meter (J&W Scientific model ADM 2000).For flow rates above 1 L/min, a Humonics model 730 bubble meter wasused. The latter device was equipped with an electronic bubble counter.Gas analysis was performed using a Fourier transform infrared (FT-IR)analyzer and a gas chromatograph (GC). To establish reproducible,standard conditions for FT-IR gas analyses, a constant, low-flow slipstream (10 ml/min) was withdrawn from the effluent gas, and a digitalperistaltic pump was used for this purpose. The slip stream was dilutedwith nitrogen (1,630 ml/min) before entering a gas cell (On-LineTechnologies 20/20™ Multipass Cell maintained at 140° C.) of an FT-IRspectrometer (Bomem MB100). Water was condensed out of the effluentstream using two condensers: one for the main stream, and one for theslip stream. Concentrations of the following species were continuouslymonitored using FT-IR analysis: CO, CO₂, SO₂, CH₄, and other lighthydrocarbons.

[0075] Gas chromatographic analysis was performed on gas samplescollected in sampling bags. A Carle Series 400 AGC gas chromatograph wasused to carry out gas analysis (H₂, CO, CO₂, C₁-C₅, and C₆ or larger).The instrument was equipped with molecular sieve columns, a thermalconductivity detector (TCD) for the analysis of H₂, CO₂, CO, and lighthydrocarbon gases, and an SRI flame ionization detector (FID) for lighthydrocarbons. In addition, a HNU 421 GC was used. It was equipped with aflame-ionization detector (FID) for heavier hydrocarbons and an SRI 110flame photometric detector (FPD) for sulfur analysis. A Chromosil 330column was used, and the oven temperature was 40° C.

[0076] Experiments involving three main components of the reactionscheme (diesel pyrolysis, steam gasification of the carbon-richfraction, and combustion of the residue) were conducted and productdistributions were determined under different process conditions. Anoptimum nominal process temperature of 1,100° C. was used in mostexperiments.

[0077] More than 200 pyrolysis-gasification-combustion cycles wereperformed, and a typical pyrolysis gas composition was found to be 84mol % H₂ and 16 mol% CH₄. An average gas composition during gasificationwas found to be 55 mol % H₂, 36 mol % CO, and 9 mol % CO₂. The abovevalues do not include small quantities of nitrogen used as a carrier gasto entrain diesel and water aerosol and introduce them into the reactor.It is expected that the need for a carrier gas will be eliminated in thefinal design of the fuel processor.

[0078] Data collected in the above series of experiments were used toproduce a flow-sheet design of a diesel-processor unit compatible with a30 ft (30,000 lb) transit bus, as shown in FIG. 2, which included massand heat balances. The assumptions and results are discussed below.

[0079] It is assumed that a complete carbon conversion to CO₂ takesplace in the char-combustion step, and the effluent gas (stream No. 7)is discarded. This means that the combustion-generated CO is entirelyconverted to CO₂ to recover the heat of reaction. This may beimplemented, for example in a catalytic or non-catalytic CO oxidizer(re-burner). An alternative arrangement, wherein the carbon monoxideresulting from char combustion is directed to the shift reactor so thatmore hydrogen could be generated, might be employed. This concept wouldhave to involve a CO—O₂ separation step, however, to prevent unreactedoxygen from mixing with the hydrogen formed in the shift reactor. Such astep would add unnecessary complexity and cost to the scheme, and theconfiguration shown in FIG. 2 is, therefore, deemed more advantageous.The CO oxidizer could have the form of a catalytic re-burner, forexample, with the heat of CO-to-CO₂ oxidation transferred either to thediesel processor directly or to one of its inlet streams (e.g., water,diesel, or inlet air pre-heater) using a heat exchanger. Furthermore,the CO oxidizer could be coupled with, or complemented by, aheat-recovery unit in which excess hydrogen from the outlet of the fuelcell is combusted. (Fuel cells usually operate under 20-25% excesshydrogen to keep the cell well purged and avoid contamination.)

[0080] In addition to the steam reformer and the shift reactor, thefuel-processing system is equipped with sulfur and carbon-monoxideremoval units to ensure adequate gas purity for the downstream units(the steam reformer, the shift reactor, and the fuel cell). Such unitsare commonly utilized in fuel-cell systems, and the design or selectionof these parts of the system is not the subject of this invention.

[0081] System response to transient changes in the feed rate andtemperature is an important consideration related to start-up andpart-load operation. Rapid start-up should be possible, e.g., by theinitial heating of the reactor with a hydrogen flame. A small hydrogenreservoir could be used to store hydrogen for the next cold start-up.Another option would involve the combustion of small amounts of dieselfuel for start-up purposes. Part-load operation could also befacilitated by computer control of cycle characteristics, such as theamount of diesel injected, duration of pyrolysis, gasification, andcombustion steps, etc. The use of energy-storage devices, such asflywheels, batteries, or ultracapacitors, is also a possibility.

[0082] The basis for the mass-balance computations was a flow of 2,050mol H₂/hr, which is an approximate nominal hydrogen demand of a 30,000lb transit bus powered with a fuel cell (Fisher, J., “Fuel cell-poweredtransit bus development,” Preprints of the Annual Automotive TechnologyDevelopment Contractors' Coordination Meeting, vol. I, Dearborn, Mich.,Oct. 23-27, 1995). Additional assumptions upon which the mass and energybalance computations were performed are listed below.

[0083] In the steam-gasification step, a steam-to-carbon ratio of 3.0 (gH₂O/g C)=2.0 (mol H₂O/mol C) was assumed based on the literature datafor steam-gasification processes (Dainton, A. D., “Gasification ofCoal,” Ch. 7 in Coal and Modern Coal Processing: An Introduction, Pitt,G. J. and Millward, G. R., Eds., Academic Press, London, 1979, pp.133-162; and Van Fredersdorff, C. G. and Elliott, M. A., “CoalGasification,” Ch. 20 in Chemistry of Coal Utilization, SupplementaryVolume, H. H. Lowry, Ed., John Wiley & Sons, New York, 1963, pp.892-1022).

[0084] In the methane reformer, a steam-to-methane ratio of 3.375 (gH₂O/g CH₄)=3.0 (mol H₂O/mol CH₄) was assumed based on the literaturedata for steam-reforming of methane (Tedder, J. M., Nechvatal, A., andJubb, A. H., Basic Organic Chemistry, Part 5: Industrial Products, JohnWiley & Sons, London, 1975).

[0085] 20% excess oxygen in the char-combustion step.

[0086] The amount of water in the shift reactor (a sum of H₂O in streamsNo. 5, 9. and 10) was assumed to be at least 1.5 times the equilibriumvalue required for the desired CO conversion (80%).

[0087] The energy required to heat reactants to reaction temperature wasunaccounted for, assuming that most of this heat could be recovered fromthe products. Although some heat loss is inevitable, it should be bornein mind that additional energy will be available from the fuel cell (anexothermic process), and also from the combustion of excess hydrogenexiting the fuel cell. In addition, the conversion of CO in the shiftreactor was assumed to be only 80%, which is very conservative andcharacteristic of a single-stage shift reactor (Austin, G. T., Shreve 'sChemical Process Industries, Fifth edition, McGraw-Hill, New York,1984). The water-gas shift reaction often proceeds nearly to itsequilibrium, which is associated with conversions close to, andsometimes in excess of, 90% rather than the assumed 80%.

[0088] Results of the mass and energy balance calculations aresummarized below.

[0089] The fuel requirement for the integrated system consisting of thediesel processor, a shift reactor, and a methane reformer was found tobe about 12.5 kg/hr, i.e., approximately 10.4 L/hr (2.61 gal/hr). Thiscorresponds to a hydrogen production of about 2.05 kmol H₂/hr (˜1.02 kgH₂/hr), which is appropriate for a 50 kW fuel cell. The air requirementfor the fuel-processor was found to be about 35.4 kg/hr (1.23 kmol/hr).The entire system operates with a water requirement of 22.8 kg/hr (1.27kmol/hr), i.e., 1.82 kg H₂O/kg diesel, but using water available fromthe fuel-cell exhaust can easily compensate for this deficit. If oneincludes the fuel cell in the water balance, a surplus of 14.1 kg/hr(0.781 kmol/hr) results. The fuel-processing system can be madethermally neutral, i.e., all the energy required for the process can begenerated from diesel fuel. The overall system efficiency (excluding thefuel cell) in excess of 90% was found. The efficiency is defined as aratio of the lower heating value of the hydrogen produced to the lowerheating value of diesel.

[0090] The concept was evaluated on the basis of the available data, andcomparisons with methanol reforming and partial oxidation were made. Theabove-described system was found to offer a substantial fuel-economy andoperating-cost advantage over the methanol reformer (at least a factorof two). The main advantages over partial oxidizers are a betterefficiency (93% versus 83%) and a better quality gas feedstock for fuelcell (78 mol % H₂ for the diesel processor versus 43 mol % H₂ for apartial oxidizer). The above performance data for partial oxidizers arequoted after Mitchell, W. L., Chintawar, P. S., Hagan, M., He, B. -X.and Prabhu, S. K., “Compact fuel processors for fuel cell electricvehicles (FCEVs),” ACS Div. of Fuel Chem. Prepr., 1999,44(4), 995-997.The main disadvantage of the pyrolysis-based diesel processing systemappears to be its relative complexity.

[0091] Thus, it can be seen that the present invention provides a novelmethod for producing hydrogen gas from a hydrocarbonaceous material. Italso provides a power system wherein hydrogen gas for use in a fuel cellis produced from a hydrocarbonaceous material, and wherein the systemmay be self-contained and implemented in a transport vehicle.

Having thus described the invention what is claimed is:
 1. A method forproducing hydrogen gas from ahydrocarbonaceous material, using reactionapparatus that includes means for absorbing and releasing thermal energyand having a heat-transfer surface, comprising the following steps,carried out cyclically: (a) bringing a quantity of a hydrocarbonaceousmaterial into contact with said heat-transfer surface of said means forabsorbing and releasing thermal energy, heated to a temperature T_(max),to effect pyrolysis thereof and thereby to produce quantities of solidcarbon-rich residue and hydrogen gas; (b) effecting combustion of atleast a first portion of said quantity of said carbon-rich residueproduced in said pyrolysis step; and (c) utilizing at least a portion ofthe thermal energy produced in said combustion step to heat said meansfor absorbing and releasing thermal energy to said temperature T_(max),for effecting said pyrolysis step in the next succeeding cycle of saidmethod.
 2. The method of claim 1 including the additional step of (d)effecting steam gasification of a second portion of said solidcarbon-rich residue produced in said pyrolysis step and deposited onsaid heat transfer surface.
 3. The method of claim 2 wherein, subsequentto said pyrolysis step, steam is introduced into the reaction apparatusfor reaction with said second portion of said solid carbon to effectsaid steam gasification step, and wherein the sensible heat of the meansfor absorbing and releasing thermal energy supplies the heat necessaryfor said gasification step, said portion of thermal energy produced insaid combustion step and used for heating said means for absorbing andreleasing thermal energy being sufficient to supply the energy necessaryfor both said pyrolysis step and also said steam gasification step. 4.The method of claim 1 wherein a quantity of carbon monoxide is produced,directly or indirectly, from said hydrocarbonaceous material, andwherein said method includes the additional step of (e) effecting awater-gas shift reaction, utilizing at least a portion of said quantityof carbon monoxide produced, so as to produce carbon dioxide and anadditional quantity of hydrogen gas.
 5. The method of claim 1 including,in said next succeeding cycle, the additional step of (f) effectingsteam reforming of gaseous hydrocarbons produced in said pyrolysis step.6. The method of claim 5 wherein thermal energy produced in saidcombustion step supplies the energy necessary for effecting said steamreforming step.
 7. The method of claim 1 wherein said means forabsorbing and releasing thermal energy comprises a bed of a catalystthat is effective for promoting pyrolysis of said hydrocarbonaceousmaterial.
 8. A method for producing hydrogen gas from ahydrocarbonaceousmaterial, using reaction apparatus that includes means for absorbing andreleasing thermal energy and having a heat-transfer surface, comprisingthe following steps, carried out cyclically, (a) bringing a quantity ofa hydrocarbonaceous material into contact with said heat-transfersurface of said means for absorbing and releasing thermal energy, heatedto a temperature T_(max), to effect pyrolysis thereof and thereby toproduce quantities of solid carbon-rich residue and hydrogen gas; (b)effecting combustion of at least a first portion of said quantity ofsaid carbon-rich residue produced in said pyrolysis step; (c) utilizingat least a portion of the thermal energy produced in said combustionstep to heat said means for absorbing and releasing to said temperatureT_(max), for effecting said pyrolysis step in the next succeeding cycleof said method; and (d) effecting steam gasification of a second portionof said quantity of carbon-rich residue produced in said pyrolysis step.9. The method of claim 8 wherein, subsequent to said pyrolysis step,steam is introduced into the reaction apparatus for reaction with saidsecond portion of said solid carbon to effect said steam gasificationstep, and wherein the sensible heat of the means for absorbing andreleasing thermal energy supplies the heat necessary for saidgasification step, said portion of thermal energy produced in saidcombustion step and used for heating said means for absorbing andreleasing thermal energy being sufficient to supply the energy necessaryfor both said pyrolysis step and also said steam gasification step. 10.A power system comprising: a fuel cell, which utilizes hydrogen forpower generation; and reaction apparatus for producing hydrogen gas,said reaction apparatus being operatively connected for deliveringhydrogen gas produced thereby to said fuel cell, and including: meansfor absorbing and releasing thermal energy and having a heat transfersurface; means for introducing a hydrocarbonaceous material into saidapparatus and for depositing the material upon said heat transfersurface for effecting pyrolysis of the material; and means forintroducing an oxygen-containing gas into said apparatus for effectingcombustion of carbon produced by pyrolysis of the depositedhydrocarbonaceous material, and for thereby delivering thermal energy tosaid means for absorbing and releasing thermal energy.
 11. The system ofclaim 10 wherein said system is self-contained.
 12. The system of claim11 additionally including means for storing a supply ofhydrocarbonaceous material operatively connected to said means forintroducing thermal energy.
 13. The system of claim 12 comprising atransportation vehicle.